In some conventional systems, a transmitter may broadcast radio frequency (RF) signals. Generally, RF signals are generated by upconverting baseband signals to intermediate frequency (IF) signals, and then further upconverting the IF signals to RF signals. The RF signals may be amplified by power amplifiers before being transmitted by a transmit antenna. Due to the proliferation of wireless devices such as telephones, walkie-talkies, personal digital assistants (PDAs), and routers in home computer networks, a strong transmitted signal with a particular operating frequency band may cause interference for wireless devices operating within the same frequency band or other neighboring frequency bands.
Frequency reuse may be utilized to minimize the impact of interference between neighboring frequency bands. With frequency re-use, multiple transmitters may be assigned to utilize the same frequency, as long as the transmitters are far enough away from each other that their transmitted signals do not interfere with each other. The most common example of frequency re-use today may be cellular communication networks utilizing time-domain multiple access (TDMA) standard. In this regard, the same frequency is utilized in cells that are not in close proximity with each other so as to minimize the effects of interference. The network operators take much care in ensuring that various frequency bandwidths are spread out among the plurality of cells such that transmitted signal in one cell does not overpower other transmitted signals of the same frequency in other cells. Other frequency re-use examples are radio stations and television stations. The Federal Communications Commission (FCC) strictly regulates the broadcasting frequencies of the radio and television stations in order to keep neighboring stations from interfering with each other. The FCC also regulates the power output of the transmitting stations in order to keep distant stations from interfering with local stations that may be broadcasting at the same frequency.
In other instances, all transmitters may transmit in the same frequency bandwidth, but, still, care must be taken to ensure that no “rogue” transmitter transmits at too high power to “drown out” other transmitted signals. Code division multiple access (CDMA) system is an example where all transmitters transmit over the same frequency bandwidth. In CDMA, special algorithms are used to code and/or decode a specific signal of interest to a transmitter and/or a receiver. Although all receivers may receive the transmitted signals, when a receiver's specific decoding code is utilized by a receiver, all other signals except the desired signal appears as random noise. However, if a transmitter transmits too much power, then that signal would appear as too much noise to other receivers, and the desired signals at other receivers may be drowned out by the noise. Therefore, a transmitted signal must be transmitted with enough power to be able to be received and decoded by a receiver, and yet must not have too much power that it interferes with other signals.
Generally, controlling output power of a transmitter is extremely important to minimize interference with other transmitted signals while still providing enough transmitted signal strength to be able to be received and processed by a receiver. In addition, a transmitter of limited power source, for example, mobile communication handset with a small battery, may need to accurately control power output in order to maximize battery life. However, a problem is that performance of various electronic devices, for example, resistors or semiconductor devices on integrated circuits may be affected by temperature. As temperature rises, a resistor's resistance may increase, thereby affecting current and voltage, and vice versa as temperature decreases. Similarly, the current that a transistor on a chip may conduct may vary as temperature changes. The change in voltage and/or current may affect the transmitter output power.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.